This invention relates to wireless transmitters and, in particular, to a technique for extending the battery life in such a transmitter.
Extending battery life is a key concern for users and manufacturers of cellular telephones and other portable transceivers. A powerful signal generated and transmitted by the wireless transceiver draws more power from the battery than when a lower power signal is generated and transmitted. Accordingly, a number of prior art techniques have been employed to adjust the gain of a portable transmitter so as to not transmit a signal more powerful than necessary for adequate communications. Examples of such ways of automatically adjusting the output power level of a transmitter are described in U.S. Pat. Nos. 4,760,347, 5,129,098, and 5,446,756, incorporated herein by reference.
Although the prior art techniques selectively reduce the output power of the transmitter, the efficiency of the transmitter is not improved by the prior art methods. The transmitter is typically biased, and operating voltages are set, so that the transmitter output signal will not distort in an adverse way at the highest expected output signals. These worse case operating conditions can draw significant power from the battery even when no signal is being transmitted. Such worst case operating conditions are not required when the transmitter is not transmitting its maximum signal. Hence, the transmitter""s efficiency is lower when transmitting lower power output signals. A lower efficiency equates to wasting battery power, reducing talk time.
What is needed is a technique for extending the battery life in mobile wireless applications.
A technique is described herein which dynamically reduces the operating voltage applied to a transmitter""s power amplifier in a mobile wireless transceiver so as to increase the efficiency of the transmitter when the transmitter is not outputting its maximum output power. Thus, the total power consumption of the transmitter is reduced as compared to prior art transmitters. In another embodiment, the bias voltage or bias current levels within the transmitter are also varied to optimize the efficiency of the transmitter at a particular output power level. This technique of controlling the transmitter""s operating voltage and bias voltage/current may be used in conjunction with conventional techniques for automatically reducing the gain of the transmitter.
In a preferred embodiment, a highly efficient switching regulator is controlled by a control circuit to adjust the operating voltage and bias voltage/current for the power amplifier in the transmitter. The control circuit has as its input any of a variety of signals which reflect the actual output of the transmitter or the desired output power of the transmitter.